Electric heating apparatus of fluidized electro-conductive powder resistance



March 13, 1962 YUKIO TANAKA 3,025,385

ELECTRIC HEATING APPARATUS 0F FLUIDIZEID ELECTRO-CONDUCTIVE POWDERRESISTANCE Filed Oct. 19, 1959 INVENTOR- Y YUK/O TA NAKA. W M

United States Patent M Japan Filed Oct. 19, 1959, Ser. No. 847,372Claims priority, application Japan Apr. 27, 1959 2 Claims. (Cl. 21950)This invention relates to an electric heating apparatus.

For heating apparatuses are conventionally used salt baths, resistancefurnaces, arc furnaces, induction heating furnaces and Criptle furnacesand so on. However, these have respectively the following defects:

Salt baths have defects that salt will be consumed and will adhere tothe heated piece; that it is necessary to select the kind of salt inaccordance with the kind of the piece to be heated and the heatingtemperature; that, if water is dropped into the bath, there is a dangerof causing the explosion of the salt; that therefore the operation andmaintenance of the bath are difficult and that the running cost of thebath is high.

Resistance furnaces have defects that, as heat generation by electricresistance is utilized in the furnace; that therefore thermal efiiciencyis low and that the maintenance of the furnace is difiicult.

Arc furnaces have not only the same defects as of resistance furnacesbut also defects that the operating temperature is too high; that thetemperature control is extremely diificult and that the thermalefficiency is low.

Induction heating furnaces have defects that the erection cost orinitial cost of the electric source and others is enormous and that theoperation is difiicult.

Criptle furnaces wherein heat generation by carbon particles is utilizedhave defects that it is difficult to insert the piece to be heated intothe furnace; that the heating is not performed uniformly, that a reactordevice causing the drop of power factor is required in order tocompensate the negative resistance characteristic of carbon.

The principal object of the present invention is to provide a heatingapparatus wherein relatively high temperature heating is possible,temperature control is easy and the control range of temperature isWide.

A further object of this invention is to provide a heating apparatuswhich is easy to operate and can be manufactured at a low cost.

Another object of this invention is to provide a heating apparatuswherein, even if the piece to be heated is irregular in shape, it can beheated uniformly.

According to the present invention, there is provided a heatingapparatus comprising a chamber containing an electro-conductive powderand having a micro-porous bottom wall Within, means to fiuidize theelectro-conductive powder within said chamber by feeding a gas throughsaid micro-porous bottom wall and electrodes to flow an electric currentthrough said fluidized electro-conductive powder.

The micro-porous bottom wall in the above described invention is suchas, for example, a porous tile plate which in nature can pass any gasbut can not pass any electro-conductive powder. The electro-conductivepowder may be a carbon powder the particle size of which is determinedby the specific gravity and otherphysical properties of the powdermaterial but may be, in short, adapted to fluidization. For example, thegrain size of about 100-150 meshes is preferable. The gas pressure to beused to fluidize the carbon powder is different depending on thethickness and porosity of the microporous bottom wall but may be ofcompressed air of about 4-10 kg./crn. As a fiuidizing gas, air isusually 3,025,385 Patented Mar. 13, 1962- used, but nitrogen or otherinert gas may be used in case oxidization is to be avoided. The shape ofthe electrode is preferably such as will make the current density in thechamber as uniform as possible. It is possible to improve the flow ofthe electric current by using auxiliary electrodes. The electric currentto be used is an alternating current of any frequency but may be adirect current.

The present invention shall now be explained with reference to theaccompanying drawing so as to be well understood.

The drawing is a longitudinally sectioned elevation of a heatingapparatus according to the present invention. 1 is a fluidizing chamberfor the heating of piece. 2 is a bed of electroconductive (carbon)powder particles floating in fiuidizing chamber 1. 3 and 4 areelectrodes dipped into the bed of carbon powder 2. 5 is an electricsource connected to electrodes 3 and 4. 6 is a micro porous bottom wallfitted in the bottom of the fluidizing chamber 1. Micro-porous bottomwall 6 is made of such material as will freely pass air but will notpass the electro-conductive powder. 7 is an air inlet provided in thebotom of the fluidizing chamber 1.

When a compressed air source is connected to the air inlet 7, air willflow in the direction indicated by the arrows and the carbon powder willbe fluidized in the fluidizing chamber. A piece to be heated notillustrated is dipped in the bed of carbon powder by being insertedbetween the electrodes 3 and 4 in the fiuidizing chamber. In such state,the carbon powder will be fluidized and move so that the particles maycome into and out of contact with each other as if in the case ofmolecular motions.

In such case, if the electric source 5 is connected to the electrodes 3and 4 and an electric power is fed, an electric current will flowthrough the carbon powder. Therefore, the carbon powder will generateheat due to said electric current and the piece to be heated locatedbetween the electrodes will be heated by the heat thus generated.

The exothermic mechanism in this case can be considered to be asexplained in the following:

Such Ioules heat as is caused by the resistance of the carbon powderitself and the contact resistance between the powder particles will bethe element of heat generation. When the powder is fluidized with air ata high temperature, heat will be generated even by the exothermicreaction caused. by chemical reaction between carbon and oxygen in theair. In such case, carbon will be consumed but heat will be generatedinstead. Therefore, even though a carbon powder is used, it will presentno negative resistance characteristic, and will act as a pure resistanceload.

As seen from the above explanation, a piece to be heated is dipped inthe fluidized powder in the chamber. Therefore, the resistance ofdipping and removal into and from the heating space is very low and theoperation is quite easy. Further, even if the shape of the piece to beheated is irregular, the contact of the piece with the fine carbonpowder in the fluidized state will be uniform. Therefore, the piece canbe uniformly heated irrespective of its shape.

The carbon will remain stable at high temperatures and therefore thepiece to be heated will be able to be heated from a low temperature to ahigh temperature above 1000 C. If the chamber is filled with an inertgas to be used to fluidize the fine electro-conductive powder, the pieceto be heated will be able to be heated up to about 1800 C.

The apparatus of the present invention can be used for a carbonsintering device. It can be used for a steel nitriding furnace by theuse of ammonia gas as the fluidizing medium. The temperature control isso easy that the apparatus can be used also for a thermostatic bath.

According to my experiments, when a carbon powder of about 150 mesheswas used, a copper plate of a surface area of 50 cm. was used for eachelectrical, the distance between the electrodes was made 5 cm., a poroustile plate was used for the micro-porous bottom wall, the plate was 30mm. thick though its porosity could hardly be numerically defined and analternating current of 100 volts, 50 cycles was impressed betweenelectrodes and intensity of current flowed between the electrodes was100 amperes, and gas pressure of air was 7 kg./cm. heat was generated upto the temperature of the electro-con iuctive powder of about 1300 C.The state of the fluidized powder at that time Was 40% higher comparedwith the case when the fluidization is not occurred.

By inserting a crucible, for example a carbon crucible, in suchfiuidizing chamber, it is possible to melt even billets in this carboncrucible.

The above described example is merely for illustration and should not beconstrued to limit the present invention set forth in the appendedclaims.

What is claimed is:

1. A heating apparatus comprising a chamber having a micro-porous bottomwall within, a bed of electroconductive powder particles supported onsaid microporous bottom wall, means for fluidizing the bed of powderparticles within said chamber by feeding a gas upwardly through saidmicro-porous bottom wall, and electrodes to flow an electric currentthrough said fluidized bed of powder particles.

2. A heating apparatus comprising a chamber having a mirco-porous bottomwall within, a bed of electroconductive carbon powder particlessupported on said micro-porous bottom wall, means to fiuidize the powderwithin said chamber by feeding a gas upwardly through said micro-porousbottom wall and electrodes to flow an electric current through saidfluidized powder.

References Cited in the file of this patent UNITED STATES PATENTS441,401 Dewey Nov. 25, 1890 749,418 Acheson June 12, 1904 FOREIGNPATENTS 689,165 France May 26, 1930 801,653 Great Britain Sept. 17, 1958UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,025,385 March 13, 1962 Yukio Tan'aka It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 4, lines 11 and 14, before "powder", each occurrence insert bedof carbon Signed and sealed this 19th day of June 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L- LADD Commissioner of Patents Attesting Officer

1. A HEATING APPARATUS COMPRISING A CHAMBER HAVING A MICRO-POROUS BOTTOMWALL WITHIN, A BED OF ELECTROCONDUCTIVE POWDER PARTICLES SUPPORTED ONSAID MICROPOROUS BOTTOM WALL, MEANS FOR FLUIDIZING THE BED OF